The mean corpuscular volume (MCV) is a standard laboratory measurement that provides specific information about the body’s red blood cells. It is one of several values calculated as part of a routine Complete Blood Count (CBC), a common panel of tests used to assess overall health. The MCV indicates the physical characteristics of the oxygen-carrying cells in the bloodstream. By focusing on cell size, this measurement helps medical professionals categorize and narrow down the potential causes of blood disorders.
What MCV Measures
The Mean Corpuscular Volume is a quantification of the average size and volume of a person’s red blood cells (erythrocytes). This measurement is typically expressed in femtoliters (fL). The size of these cells reflects how successfully they are formed in the bone marrow and how efficiently they transport oxygen throughout the body.
Automated hematology analyzers measure this volume by analyzing thousands of red blood cells in a sample, providing an average value. Cells that are too small or too large may not carry sufficient oxygen, leading to symptoms like fatigue or shortness of breath. The MCV is a fundamental tool for classifying blood disorders based on the size of the circulating red cells.
When Doctors Order the MCV Test
The MCV is not usually ordered as a standalone test; it is an automatic component of the routine Complete Blood Count (CBC). Doctors frequently order a CBC during annual physical examinations as a broad screening tool to check general health. The CBC provides a snapshot of the blood’s components, including red cells, white cells, and platelets.
The MCV is also ordered when a patient reports symptoms that might suggest a blood disorder, such as persistent fatigue, pallor, or dizziness. It is utilized to monitor the progression of known blood conditions and to assess the effectiveness of ongoing treatments. The MCV helps guide further diagnostic steps.
Interpreting a Low MCV Result
A low MCV result (below 80 fL) indicates that the red blood cells are smaller than average, a condition called microcytosis. The most frequent cause of microcytosis is Iron Deficiency Anemia, the most common form of anemia worldwide. Iron is necessary for the production of hemoglobin, the protein responsible for binding oxygen.
When iron is scarce, the body cannot synthesize enough hemoglobin, causing the red blood cell precursors to undergo extra divisions, resulting in a smaller cell size. Other causes of microcytosis include Thalassemia, a genetic condition that impairs the production of hemoglobin chains, and Anemia of Chronic Disease. In Anemia of Chronic Disease, long-term inflammation interferes with the body’s ability to use stored iron. Identifying a low MCV directs the physician to run additional tests, such as iron studies, to confirm the underlying cause.
Interpreting a High MCV Result
A high MCV result (above 100 fL), or macrocytosis, signifies that the red blood cells are larger than normal. The most common cause involves deficiencies in Vitamin B12 and Folate (Vitamin B9). Both nutrients are necessary cofactors for the synthesis of DNA within developing red blood cells.
A lack of Vitamin B12 or Folate impairs DNA production, disrupting the normal cell division process in the bone marrow. This failure to divide properly leads to the release of large, immature red blood cells, known as megaloblasts, into the bloodstream. Other factors contributing to macrocytosis include chronic alcohol use, which affects red blood cell formation, and various types of liver disease. Certain medications can also interfere with cell division, leading to an elevated MCV.